Berlin was starting out its new life as a divided city, with the Eastern half in Soviet hands and the West under Allied control. Stalin, however, wasn't about to settle for half of the cake. He blockaded Berlin from all Western military and civilian traffic, a particularly effective dick move, since West Berlin was completely surrounded by the wholly communist German Democratic Republic. Thus, Stalin was effectively giving the Western powers a giant middle finger ... and also about a month until the surrounded West Berlin would begin to starve.
Stalin never wanted to start a war with the West. However, he needed to appear strong, which, with his particular modus operandi, required constant tension with his opponents. However, the United States still remembered the previous mustachioed lunatic ranting about Berlin, and was totally ready to rumble. General Lucius D. Clay, the head of the Occupation Zone in Germany, advocated sending an armed convoy to battle their way into Berlin ... through East Germany. Effectively going to war with the Soviets, in other words.
Lucius Clay, seen here looking like a screengrab from Dr. Strangelove.